1. Field of the Invention
The present invention relates to a system for purifying a polluted air including carbon dioxide, nitrogen oxide and/or sulfur oxide by using algae such as Spirulina. This system can be used to provide a purified air to multipurpose facilities such as theater, department store, super market, hotel, conference hall, hospital, bank, office building, subway station, and underground shopping center.
2. Disclosure of the Prior Art
In recent years, air pollution caused by exhausts from thermal power plants, automobiles and so on is becoming serious in every country of the world. The exhausts usually contain poisonous gas components to the human body, for example, sulfur dioxide (SO.sub.2), nitrogen oxide (NO.sub.x) and carbon monoxide (CO). In particular, nitrogen oxide is very poisonous to the human body, and gives a bad influence to nasal cavity, throat, trachea, bronchiole, alveolus, and blood vessels. In addition, it is known that nitrogen oxide gas induces a photochemical smog under a weather condition. Since the nitrogen oxide gas has a relatively large specific gravity, it is said that the air pollution is more serious in the underground shopping center or subway station. In particular, when a heavy traffic density of cars occurs at roads built above subway, the air around the roads is badly polluted by the exhausts of automobiles. The quality of air in the subway station is getting increasingly worse by the badly polluted air flowing from the outside into the subway. In fact, diseases such as allergic disease, atopic dermatitis, asthma, lung cancer, and stomatitis increase in city areas. It is said that the air pollution is one of causes of these diseases. By a conventional filtration, dust can be removed from the polluted air flowing into the underground facilities. However, it is very difficult to remove NO.sub.x and SO.sub.x gas components from the polluted air by the filtration.
In addition, crowd gathers in multipurpose facilities such as theater, department store, super market, hotel, conference hall, hospital, bank, office building, subway station, and underground shopping center. As oxygen is consumed in the facilities, the concentration of CO.sub.2 in the air relatively increases. This gives fatigue or unpleasant feeling to people utilizing the facilities.
By the way, increasing CO.sub.2 is a worldwide problem as it is considered to be a main cause of global warming. The concentration of CO.sub.2 in the air was 270 ppm at the time of Industrial Revolution. Now, it has increased up to 350 ppm as a result of increasing use of fossil fuel. This means 130% increase during about 200 years. In general, it is regarded that 31 % of the entire CO.sub.2 sources come from thermal power plants, 17% from transportation such as automobiles, and 12% from public utility excluding electricity (e.g. town gas). According to some research, the concentration of CO.sub.2 would double and average temperature would rise by 1.5-3.0 degrees by the year 2030 if CO.sub.2 continues to increase at the present pace.
In the past, an air purifying system for removing suspended particles of dust by a filter, or ionizing and adsorbing the suspended particles of dust has been proposed. It is also proposed to adsorb bad-smell components in the air by using an activated carbon layer. However, NO.sub.x and SO.sub.x gas components can not be substantially removed from the polluted air by these systems.
Thus, it is desired to provide a system for efficiently purifying a polluted air including carbon dioxide, nitrogen oxide, and/or sulfur oxide. However, an epoch-making means of satisfying the demand has not been proposed yet.